Why horn-loaded loudspeakers are subject to design tradeoffs

[Deang]

I'm disappointed to hear that about the kit. Really.

[Deang]

"The CBT kit from Parts Express is really cool in demonstrating the concept, but it doesn't go very loud at all and sounds like a classic direct radiator system: distortion and all."

I'm disappointed to hear that about the kit. Really.

[mark1101]

This was interesting to read. Check it out. Assembly of the Parts express CBT kit.

http://www.amb.org/forum/new-speaker-fi-audio-artistry-cbt36-t1887.html

[mark1101]

After reading the whole thing from stem to stern my take is that CBT is nothing more than a FAD............just like Maggies were. Certainly no powerhouse speakers and only play down to 45Hz. Maybe the coverage is good. That seems to be their bragging rights.

Don Keele recommends the Behringer 2496DCX processor ............since they have to be run actively. (Sorry Dean). That recommendation right there tells me the speakers are not going to sound very good.

Half the discussion is "upgrading" the processor unit.

Don't sell your subs..........

[ClaudeJ1]

"The CBT kit from Parts Express is really cool in demonstrating the concept, but it doesn't go very loud at all and sounds like a classic direct radiator system: distortion and all."

I'm disappointed to hear that about the kit. Really.

I disagree with this comment. His idea of loud is horns with Kilowatts in a gymnasium. Nothing personal, Mike but that is just your own biased opinion, no better or worse than my own biased opinion. At least I try to look for the good in things.

The CBT was demonstrated in an AUDITORIUM and could be heard clearly from 100 feet back. I'm sure that in a home environment, it would be operated at 1/10th the power input, with distortion no worse than a pair of Heresy's. Even with a lotta watts going through them, I though they sounded really good. The amazing part is that they seem to violate the inverse square law. There simply has been NOTHING that sounds like the CBT before. A deep and solid stereo image no matter where you were standing. Whether up, down, or to the sides, the volume didn't change. The most uncanny thing I have ever experienced. You are merely listening to one person's biased opinion. I was standing next to Mike at the demo and he made a negative comment to me, while all the other engineers in the room, including me, were amazed.

So basically, it's this. No demo in the "wrong room" can ever give any speaker a fair shake whether the room is too small, like at Axpona, or too big, at Shure headquarters.

[ClaudeJ1]

After reading the whole thing from stem to stern my take is that CBT is nothing more than a FAD............just like Maggies were. Certainly no powerhouse speakers and only play down to 45Hz. Maybe the coverage is good. That seems to be their bragging rights.

Don Keele recommends the Behringer 2496DCX processor ............since they have to be run actively. (Sorry Dean). That recommendation right there tells me the speakers are not going to sound very good.

Half the discussion is "upgrading" the processor unit.

Don't sell your subs..........

Not true. I had lunch with Don 2 days ago, and he recommends Mini DSP's. The only reason he used the Behringer was ease of use, low cost, and availability at the time of development. He recommends the user use the best electronics possible, but what he REALLY wants is to go with PASSIVE 2-way, NOT active.

Plus he's 73 and admits he can't hear above 9 Khz.. so he can't speak to audibility of different active Xovers. BTW, even though his name is not on the patent, he worked on the MWM woofers with Gary Gillum while he was at Klipsch. He did verify they were developed with K-33's to me, like I have maintained for years after interviewing G.G. 6 years ago.

CBT's need subs, like all horn speakers, and aside from Synergy Horns from Danley, they are the only TRUE constant directivity speakers at all frequencies above 160 Hz. The distortion goes down radically when you cross them at 100 Hz. to a sub instead of boosting the low end at 45 Hz. You have 18 voice coils on the 18 woofers, which are equal to a 12" driver, but with 18 Neo Magnet motors, the transient response, while not horn loaded, is better than any single motor Direct Radiator.

Their unique sonic presentation makes them the very best speaker for surround channels in a home theater.

You don't use a screwdriver as a hammer or vice versa, or put round pegs in square holes, so the APPLICATION of any device in a relative sense is better than any kind of absolute proclamations under the veil of strong biased opinions.

Edited July 24, 2014 by ClaudeJ1

[ClaudeJ1]

I probably won't get any opportunity anytime soon to hear a CBT. So, I wonder how it compares in sound (conceptually) to a near field monitor? I gather the idea here is about the wave front presented to listener. So, does this wave front differ conceptually from that which I would get from a near field setup?

It looks like it is designed to present uniform waves to a larger physical space. e.g. allows people to sit in various places and hear the same thing. No sweet spot. That sort of thing.

You might after I build mine. You are correct about lack of sweet spot. That is the main reason for Don Keele evolving the adaptation of Navy technology to Audio and his being the EVANGELIST for their propagation of sound and number of units made. He really believes in it and he revolutionized horn design at EV and JBL, so he has full credibility with me.

Edited July 24, 2014 by ClaudeJ1

[ClaudeJ1]

So, looking at those two pictures posted by Max2 of the CBT-----

Are they the size they are because that's what transducers are available?

Or, because they are intended to be in a certain sized room?

Or, because that is some ideal size for the CBT effect to be heard?

When I look at the pictures, I get the impression that they would have optimum sound only under some optimum setup - like most speakers.

Is there an ideal CBT perhaps made with much small transducers? Much larger? What does the principle dictate?

Yes. Yes, like any other speaker. Yes, smaller, more closely spaced drivers, give you the best dispersion characteristic, but wheter you suspend or use floor reflections, like the units in the photos, you must reduce the intensities shown in the models (Legendre shading). Don is working on simplifying things even more as part of R&D right now.

Smaller or larger transducers, 2-way with Xover, Single driver arrays, etc. are subject to trade-offs similar to other devices that, basically, vibrate air.

[Marvel]

You could read all the info on the JBL site for their CBT arrays. The idea, of course, is for very even coverage over the entire listening area. For an auditorium, it should mean that walking up to the stage, you have the same level as the back of the room. Our school was looking at them for installation in our chapel/auditorium. It's a terrible cave of a room and acoustics are terrible, with a 60 foot high ceiling and odd shape. JBL folks from Atlanta were supposed to bring some stuff up to demo, but the idea got dropped somewhere along the way.

Bruce

[Deang]

Half the discussion is "upgrading" the processor unit.

Gee, that's a surprise.

[ClaudeJ1]

Half the discussion is "upgrading" the processor unit.

Gee, that's a surprise.

Don told me he prefers a passive solution. How's THAT for a surprise!

[Max2]

Most bands have been using these curved arrays for a while now, isn't it close to the same thing? Also, while everyone here seems to think that if your bass cab is not horn loaded, its close to crap. Why the gushing over these? It seems like they are taking a direct setup and creating a dispersion pattern like a horn only on broader scale. Even then, will have the dynamics of a horn? You will also need some serious power to feed all the drivers, yes?

[Don Richard]

The CBT seems to be an implementation based on "line array" technology, specifically curved arrays, but on a smaller scale. Some of the best concert sound I've heard was a JBL system curved through it's entire length at an outdoor amphitheater. It sounded the same wherever you were, up, down, left to right, even by the concession stands on the sides of the seats.

[DrWho]

"The CBT kit from Parts Express is really cool in demonstrating the concept, but it doesn't go very loud at all and sounds like a classic direct radiator system: distortion and all."

I'm disappointed to hear that about the kit. Really.

I disagree with this comment. His idea of loud is horns with Kilowatts in a gymnasium. Nothing personal, Mike but that is just your own biased opinion, no better or worse than my own biased opinion. At least I try to look for the good in things.

The CBT was demonstrated in an AUDITORIUM and could be heard clearly from 100 feet back. I'm sure that in a home environment, it would be operated at 1/10th the power input, with distortion no worse than a pair of Heresy's. Even with a lotta watts going through them, I though they sounded really good. The amazing part is that they seem to violate the inverse square law. There simply has been NOTHING that sounds like the CBT before. A deep and solid stereo image no matter where you were standing. Whether up, down, or to the sides, the volume didn't change. The most uncanny thing I have ever experienced. You are merely listening to one person's biased opinion. I was standing next to Mike at the demo and he made a negative comment to me, while all the other engineers in the room, including me, were amazed.

So basically, it's this. No demo in the "wrong room" can ever give any speaker a fair shake whether the room is too small, like at Axpona, or too big, at Shure headquarters.

This is where experience with the S.N. Shure Theater is extremely helpful....the acoustics in that room are amazing, and tweaked towards the "acoustic amplification" of live instruments. The quietest of sounds from the front of the room can be heard almost equally everywhere. I certainly would not be ascribing your impression of the lack of inverse square law to the speaker. That was all the room.

Consequently, the power he was pouring into the speakers would be very close to a typical home environment. In fact, I recall hearing the CBT at two different hotel audio show things (was it Axpona both times? I don't remember - they all blur together). Again they were pouring in a lot of power and just not a lot of sound comes out. If you integrate the power from each speaker with the shading applied, it's equivalent to having something like two to three of each driver...not the billion the array requires - which isn't a lot when you're starting with such small drivers. With the passive version you need a ton of voltage to get any power into the system - kinda like electrostats. Unlike other line array approaches, you don't get the crazy SPLs....all those extra drivers are just filling in the gaps that would otherwise exist in the polar response.

Btw, Keele wasn't trying to make the best sounding speaker in the world when he came out with this DIY CBT design - he saw this as the best lowest entry cost to demonstrate the awesome polars that can be accomplished with the approach. Sound quality will be comparable to your typical nearfield listening setup, except you can experience it a little bit further away. The fact that you can get near perfect polars from multiple drivers solves the classic problem with crossovers - at least partially. That is where the genius in this shading approach lies.

I might also add that you're putting words into my mouth in regards to what I consider loud. I am not an SPL junky by any stretch of imagination, and take hearing loss very seriously (both for my own listening and when doing live sound). I also take my dynamics and crest factor seriously too, and try to keep them uncompressed wherever possible...crest factor is where the difference is.

[DrWho]

It sounded the same wherever you were, up, down, left to right, even by the concession stands on the sides of the seats.

....until the wind started blowing: and then it sounds like a poorly encoded mp3...gotta love them squirly highs.

[mark1101]

Forum member JWC had an expensive pair of McIntosh towers with the CBT pricinciple. Like 72 tweeters or something like that. Honestly, they were awesome and did not need subs (by the way). But they weren't some cheap kit with budget drivers and no crossover...........and JC had 1200 watt Macs driving them. Different beast.

The CBTs are just a home audio budget version of what's been around a long time in Pro sound reinforcement. Go to any concert today or back in the 80s and 90s and it's been hanging right in front of you.

Anyhow.............if you read the thread on how to assemble them there is not really anything special about them at all. It is groups of tiny budget drivers positioned along a curved baffle playing at "shaded" volumes relative to each other.

I just don't find anything interesting to me at all about it. Why dioes it amaze everyone if you can walk around the room and get even coverage? Klipsch does that with their speakers too.

[jason str]

So, thinking back to the original question about tradeoff of horn loudspeakers, I'd say the #1 tradeoff is just size. And this becomes dramatically true in a full range horn system.

I agree with this statement, size is the only downfall.

[Chris A]

So, thinking back to the original question about tradeoff of horn loudspeakers, I'd say the #1 tradeoff is just size. And this becomes dramatically true in a full range horn system.

Yes, and some complexity at the horn design level (just like designing arrays of direct-radiating line array drivers like Don Keele's design mentioned here).

It's been my experience that there are a lot of really poorly designed horns (and compression drivers, for that matter since the horns amplify any design errors that show up in compression drivers)--in terms of hi-fi reproduction measures only--than direct-radiating loudspeakers just because you need to know more things before you start tinkering.

If all you are trying to do is to cover an area with SPL in the midrange without concern for hi-fi reproduction, then there are a lot of horns that can provide this, and fairly cheaply. I'm thinking of Don Keele's constant directivity horns and the older multicell horns for PA use, in order to get better venue coverage. These particular types of CD horns all seem to use diffraction slots and other hard-edge discontinuities to achieve wide and relatively even coverage -- but at a price in terms of higher order modes [HOMs] inside the horn that make an artificial sound like "frying eggs".

This is why I really believe in Roy Delgado horns and other conical horn profiles with smooth transition throats (like Geddes and Charlie Hughes' quadratic throat waveguide) for hi-fi use, and no "slots" or other prominent hard-edges inside the horn, and non-straight-sided horns that don't sound very good off-axis.

Edited July 25, 2014 by Chris A

[Deang]

Good post.

I wish the available quadratic waveguides went lower -- didn't Peavy end up making those things?

[Chris A]

Yes: http://peavey.com/products/index.cfm/series/685/QW%C2%AE%20Series

http://www.excelsior-audio.com/Publications/QTWaveguide/QTWaveguide_WhitePaper.pdf